1. Field of the Invention
The present invention relates to a method and machine for automatically grasping two adjacent corners of a flat sheet. Such a machine is particularly suitable for operation in a laundry, after the washing phase and before the finishing phase of the flat sheet, for which phase the flat sheet must be presented while being grasped at its corners. In the finishing phase, the washed and wrung-out flat sheet, stretched between two of its adjacent corners, is engaged by a mangle that then drives it in order to dry it, press it and fold it automatically.
1. Description of the Related Art
In practice, finding the corners of a flat sheet must be done by hand, which is very labor-intensive and consequently increases the fixed costs for laundries. One system for automatically grasping flat sheets has already been described in French Patent 2336510. The system proposed there requires catching the flat sheet at four points in succession; the four points are a first point anywhere on the flat sheet, a first corner of the flat sheet comprising the lowermost point of the flat sheet suspended from the first arbitrary point, the corner of the flat diagonally opposite this first corner, and a second corner of the flat sheet adjacent to the first. Furthermore, the fact that the flat sheet is stretched between the first corner and the corner diagonally opposite it results in a machine of relatively great bulk, since the flat sheet is thus stretched on the diagonal, which is the longest distance between two points on a flat sheet. Finally, this system uses sets of detectors to find the second corner; accordingly, it must be possible for the closure of the grippers for grasping the flat sheet to be controlled at an undefined point, which is technically more difficult to accomplish than a system where closure of the grippers takes place at a fixed location.
The present invention provides a method which overcomes the foregoing disadvantages and which comprises the steps of gripping a first corner of a flat sheet after the sheet has been suspended and with the first corner being distanced from an arbitrary zone by a length greater than one-half the diagonal of the sheet. In a second step, a relative displacement by translation of the first corner while being gripped with respect to the gripping zone of the sheet is provided such that at least one of the two corners adjacent to the first corner comprises an apparent low point of the flat sheet stretched between the arbitrary gripping zone and the first corner. In a third step, the apparent low point is gripped and, in a fourth step, the portion gripped in a gripping zone is released. In the first step, the sheet is hung by gravity so as to allow a portion thereof to define the lowest point of the sheet and, in the second step, means are provided for shaking out the sheet and thereafter the sheet is positioned over a separation surface with the gripped portion and the first corner of the flat sheet disposed on either side of the separation surface.
The invention also includes apparatus for carrying out the steps of the method including a suction device for gripping the sheet during the first step and a detector to signal the passage of the lower most point of the flat sheet after a selected distance of travel. Translation paths defined by rails are provided for carrying the sheet through the subsequent steps.
Various alternative embodiments will become apparent as consideration is given to the following detailed description.